Assessing SARS-CoV-2 Neutralizing Antibodies after BNT162b2 Vaccination and Their Correlation with SARS-CoV-2 IgG Anti-S1, Anti-RBD and Anti-S2 Serological Titers

Abstract

The humoral response through neutralizing antibodies (NAbs) is a key component of the immune response to COVID-19. However, the plaque reduction neutralization test (PRNT), the gold standard for determining NAbs, is technically demanding, time-consuming and requires BSL-3 conditions. Correlating the NAbs and total antibodies levels, assessed by generalized and automated serological tests, is crucial. Through a commercial surrogate virus neutralization test (sVNT), we aimed to evaluate the production of SARS-CoV-2 NAbs in a set of vaccinated healthcare workers and to correlate these NAbs with the SARS-CoV-2 IgG anti-S1, anti-RBD and anti-S2 serological titers. We found that 6 months after vaccination, only 74% maintain NAbs for the Wuhan strain/UK variant (V1) and 47% maintain NAbs for the South African and Brazil variants (V2). Through Spearman's correlation, we found the following correlations between the percentage of inhibition of NAbs and the SARS-CoV-2 IgG II Quant (Abbott Laboratories, Chicago, IL, USA) and BioPlex 2200 SARS-CoV-2 IgG Panel (Bio-Rad, Hercules, CA, USA) immunoassays: rho = 0.87 (V1) and rho = 0.73 (V2) for anti-S1 assessed by Abbott assay; rho = 0.77 (V1) and rho = 0.72 (V2) for anti-S1, rho = 0.88 (V1) and rho = 0.82 (V2) for anti-RBD, and rho = 0.68 (V1) and rho = 0.60 (V2) for anti-S2 assessed by BioPlex assay (p < 0.001 for all). In conclusion, we found a strong correlation between this fast, user-friendly, mobile and bio-safe sVNT and the serological immunoassays.

Keywords: BNT162b2 vaccine; SARS-CoV-2; neutralizing antibodies; serological immunoassays; surrogate virus neutralization test.

Figure 1

Percentage of SARS-CoV-2 neutralizing inhibition (PI) as a function of SARS-CoV-2 IgG serological titer. The PI of NAbs for V1 (blue) and V2 (orange) are correlated with (A) anti-S1 (Abbott), (B) anti-S1 (BioPlex), (C) anti-RBD and (D) anti-S2 serological titer. The red line represents the sVNT cut-off. PI results < 20% are reported as “negative,” and PI ≥ 20% are reported as “positive”.

Figure 2

Percentage of SARS-CoV-2 neutralizing inhibition (PI) as a function of SARS-CoV-2 IgG anti-S1 in serum collected 3 months after vaccination from NAbs-negative participants. The PI of NAbs for V1 (blue) and V2 (orange) are correlated with anti-S1 (Abbott) serological titer in 8 NAbs-negative participants at 6 months after vaccination. The red line represents the sVNT cut-off. PI results < 20% are reported as “negative,” and PI ≥ 20% are reported as “positive”.

Figure 3

Mean percentages of SARS-CoV-2 neutralizing inhibition (PI) at 6 and 10 months (n = 21) after the 2nd dose and 1 month (n = 13) after the 3rd dose of Pfizer vaccine for V1 (blue) and V2 (orange). The red line represents the sVNT cut-off. PI results < 20% are reported as “negative,” and PI ≥ 20% are reported as “positive”.